effect-ts git:20261005.bc026bfB

Immutable. This exact content never changes and is served at /api/v1/blob/a1262e3c204c60f6.

---
compatibility:
  Requires a project using current stable Effect 4 packages; verify exact APIs against the target's installed package
  source. The source-cache helper needs git and network access for its daily fetch.
name: effect-ts
description:
  Use for nontrivial Effect 4 work including services/layers, typed errors, Schema/JsonSchema, Config,
  runtime/concurrency, @effect/vitest, effect/ai and @effect/ai-*, effect/sql and @effect/sql-*, Effect Atom
  (@effect/atom-*), or @prb/effect-next.
---

# Effect 4

Apply Effect 4 semantics from project-local architecture, the narrowest relevant reference, and source matching the
target's installed packages.

## Workflow

Do not activate this workflow merely because a file imports `effect`. For nontrivial Effect work:

1. Resolve the target package or workspace and its exact installed `effect` and relevant `@effect/*` versions. If
   `effect` is not 4.x, stop because this skill does not apply; for 3.x, point the user to the v3 skill:
   `npx skills add PaulRBerg/agent-skills#shelved --skill effect-ts-v3`.
2. Confirm lockstep versions: every `@effect/*` package must match the installed `effect` version exactly. Report a
   mismatch instead of coding around it.
3. Inspect neighboring services, layers, errors, schemas, runtime boundaries, and tests. Local conventions decide
   organization; installed package evidence decides API facts.
4. Read `references/critical-rules.md`, then only the task-specific references below.
5. Verify every uncertain import, signature, or behavior against the package installation visible to the target
   workspace before editing. Do not port v3 names from memory; many were renamed or removed.
6. Implement the smallest pattern consistent with the project and run the narrowest test or typecheck covering the
   changed semantics.

## Evidence Order

Use the target workspace's manifest and lockfile to identify versions. Prefer, in order:

1. the installed package's `src/`, README, tests, and changelog;
2. its emitted declarations when source is not shipped;
3. the matching official package artifact or source tag.

For monorepo source, tests, or cross-package search, run `scripts/effect-source.sh`. It keeps a cached clone of
`Effect-TS/effect` checked out at the newest release, fetching at most once per 24 hours and otherwise reusing the
cache, and prints `path=` and `release=`. When `release` differs from the installed `effect` version, read the matching
tag without checking it out: `git -C <path> grep <pattern> effect@<version> -- packages/` or
`git -C <path> show effect@<version>:<file>`. Never edit the cache.

Do not install or update dependencies solely to obtain documentation. Do not trust v3 examples or source that does not
match the target's installed version. If exact behavior cannot be verified, stop rather than guessing.

Former `@effect/platform`, `@effect/rpc`, `@effect/cli`, `@effect/cluster`, and related modules now ship inside `effect`
under subpaths such as `effect/http`, `effect/http-api`, `effect/rpc`, `effect/cli`, `effect/ai`, `effect/sql`,
`effect/schema`, `effect/reactivity`, and `effect/workflow`. Check the installed `package.json` `exports` for the exact
set. These modules are documented `@stability unstable` and may break in minor releases; there are no
`effect/unstable/*` compatibility paths. Separate packages remain for platforms, drivers, and providers:
`@effect/platform-*`, `@effect/sql-*`, `@effect/ai-*`, `@effect/atom-*`, `@effect/opentelemetry`, and `@effect/vitest`.

## Reference Router

| Task                                                | Reference                         |
| --------------------------------------------------- | --------------------------------- |
| Services, Layers, `Context.Service`, `fn`           | `references/services-layers.md`   |
| Config providers and secrets                        | `references/config.md`            |
| Schema, JSON Schema, encoded errors/models          | `references/schema-jsonschema.md` |
| `@effect/vitest`, clocks, fibers, retries           | `references/testing.md`           |
| resources, scheduling, refs, concurrency            | `references/runtime.md`           |
| streams and backpressure                            | `references/streams.md`           |
| pattern matching and tagged unions                  | `references/pattern-matching.md`  |
| `effect/ai` and `@effect/ai-*`                      | `references/ai.md`                |
| `effect/sql` and `@effect/sql-*`                    | `references/sql.md`               |
| Next.js / `@prb/effect-next`                        | `references/next-js.md`           |
| Effect Atom (`effect/reactivity`, `@effect/atom-*`) | `references/effect-atom.md`       |
| `Option` at nullable boundaries                     | `references/option-null.md`       |

For `effect/http`, `effect/http-api`, `effect/rpc`, `effect/cli`, collection utilities, deprecations, or constructor
lookup, inspect the installed package source directly instead of loading a local API inventory.

## Boundaries

- Keep pure helpers, constants, and path manipulation pure unless an Effect boundary provides a concrete dependency,
  testability, resource-safety, or error-model benefit.
- Preserve existing domain facades and service/runtime boundaries unless the user requested redesign.
- Prefer typed failures and scoped resources at IO boundaries; choose Schema-backed errors/models only when encoding or
  boundary validation is needed.
- Do not broaden environment requirements merely to replace a small platform call.

For changes, completion requires code consistent with local Effect architecture, selected references and installed
source where needed, and the narrowest test/typecheck that exercises the changed semantics. Read-only work requires
evidence for the reported conclusion. Finish with `### ⚡ Effect — ✅ change complete` after verified edits or
`### ⚡ Effect — 🔎 reviewed, no files written` for read-only work, one sentence naming the boundary or pattern used,
and `### 🧪 Verification` with exact scoped commands/results. If required validation is incomplete, use
`### ⚡ Effect — ⛔ blocked` instead. Add `### ⚠️ Limitation` only for non-blocking caveats. Never decorate typed
errors, Schema messages, logs, tests, generated JSON/API responses, or command output.